1. Field of the Invention
The present invention relates to a hydraulic reservoir and, more particularly, to a hydraulic fluid reservoir formed by rotational molding with an integral molded baffle.
2. Brief Description of the Prior Art
Rotational molding, or rotomolding, is a well-known method of forming objects from a plastic resin. It is often used for complex shapes including tanks and reservoirs. Various types of plastic resin can be used, such as polyethylenes, plastisols, nylons, fluoropolymers, polypropylenes, polyurethanes, and other suitable materials.
In general, a mold is loaded with a plastic resin and heated in an oven. As the mold is heated, the mold is rotated about two or three axes at a low speed. The heat melts the plastic resin inside the mold and melted resin coats the interior surface of the mold. The mold is then gradually cooled using air or water and the re-solidified plastic resin, which has assumed the shape of the interior walls of the mold, is removed from the mold. This process differs from injection molding in that the plastic resin is not pressurized (other than atmospheric pressure).
U.S. Pat. No. 5,285,923 illustrates the insertion of objects made of a material other than plastic resin into the object to be formed, such as brass inserts molded into a polyethylene material. In general, the insert is placed in a designated spot in the mold and the rotomolding process is initiated as described above. The melted plastic resin encapsulates the insert and the insert becomes part of the finished product. A problem is that the expansion and contraction properties of the resin and the inserted objects are not necessarily equal. Leaks or gaps can develop between the inserted object and the cooled plastic resin. This problem is amplified by the fact that plastic resin is known to shrink an appreciable amount as it cools. U.S. Pat. Nos. 3,364,292; 4,023,257; and 4,847,028; also discuss rotomolding with inserts added to the molded product. All of the above-cited references are incorporated herein by reference.
As noted in the above-cited prior art, rotomolding is well-suited for forming a plastic tank or reservoir structure. Such tanks are often used as hydraulic reservoirs for hydraulic systems, such as used in heavy machinery, including cranes, backhoes, demolition shears, bulldozers, and the like. In hydraulic systems, it is important to keep the hydraulic fluid free of debris. Consequently, filtering elements have been incorporated in the hydraulic systems to filter debris from the hydraulic fluid. Further, as set forth in U.S. Pat. Nos. 4,143,193 and 5,911,938 baffles are often incorporated into hydraulic reservoir tanks, as well as fuel tanks, to dampen the forces of moving liquid within the tank. The baffle designs suggested in these patents are formed of additional elements integrated into or integral with the finished tank. Additional holding fixtures are required during molding and these designs increase the complexity of the mold, and result in an increase in manufacturing time and expense.
It is an object of the present invention to provide a rotomolded hydraulic reservoir with an integral molded baffle. It is a further object of the present invention to provide a rotomolded hydraulic reservoir with integral filter bowl having an extended integral filter container with a coupling insert. It is another object of the present invention to provide a rotomolded hydraulic reservoir with a second fluid return. It is another object of the present invention to provide a hydraulic reservoir that is economically manufactured. It is a further object of the present invention to provide an effective, easily replaceable filter element for a hydraulic reservoir.
The above objects are achieved with a rotomolded hydraulic reservoir having an integral molded baffle according to the present invention. A baffle is a term referring to a structure that significantly affects the fluid flow in the hydraulic reservoir. The hydraulic reservoir is a one-piece tank structure. Specifically, the hydraulic reservoir includes a rotomolded one-piece, integral plastic container body defining a container cavity for receiving the hydraulic fluid. The container body has an integral molded baffle extending inwardly and formed as part of an outer wall of the container body, wherein the baffle extends at least a third of the depth of the container cavity. The container body may form the integral solid baffle within the container cavity extending from one side of the container body wherein the sides of the baffle converge toward each other from the side of the container body toward the mid-line of the container cavity at an appropriate shallow angle, such as about six degrees (plus or minus two degrees). The baffle may extend substantially across a lower portion of the container cavity with a gap in the baffle extending to a bottom surface of the container body. The baffle may extend substantially perpendicular to a longitudinal axis of the container body.
The container body may form a filter cavity in fluid communication with the container cavity. A filter element coupling insert, such as a machined metallic bushing, may be molded in the container body adjacent the filter cavity. A removable filter element is positioned within the filter cavity and coupled to the insert. The removable filter element seals to the exterior of the insert.
In order to help ensure a positive seal between the resin and the part to be included, the present invention generally provides a container body forming a filter cavity with an end having, in cross section, a bowl-shape. The insert is positioned adjacent to the cross sectional bowl-shape of the filter cavity. The bowl-shape offers controlled shrinkage tolerances in the general vicinity of the insert.
In one embodiment of the present invention, the fluid communication provided between the filter cavity and the container cavity is provided to extend to a level below the normal fluid level in the hydraulic reservoir. Additionally, a second fluid return communicating with the container cavity may be provided in one embodiment of the present invention with the second fluid return including an integral metallic coupling insert. The second fluid return may be provided with a fluid communication with the container cavity at a level lower than the fluid level within the container cavity through an extended coupling insert. A normal fluid level for a hydraulic reservoir varies between rest and operating conditions. Although dynamic, the term normal fluid level is a specific defined range unique to a given hydraulic reservoir and a given application.
One embodiment of the present invention the solid integrally molded baffle extends from the bottom and only one side of the container cavity to about one-half of the container cavity and substantially the entire width of the container cavity. A gap is provided between the other side and the baffle with the gap extending to the bottom whereby fluid at any level within the container cavity can flow around the integral baffle. Other modifications are possible. For example, the gap would be provided on both sides of the baffle or the baffle could extend on both sides of the gap.
These and other advantages of the present invention will be clarified in the description of the preferred embodiments taken together with the attached drawings in which like reference numerals represent like elements throughout.